Mixing circuit arrangement



April 3, 1952 A. VAN WEEL 2,591,983

MIXING CIRCUIT ARRANGEMENT Filed July 20, 1946 2 SHEETS-SHEET 1 (mpmwci) 1 p" IN V EN TOR. ALDERTmN MEL BYW7 7/7 AGHVI April 1952 A. VAN WEEL 2,591,983

MIXING CIRCUIT ARRANGEMENT Filed July 20, 1946 2 SHEETS-SHEET 2 Zf/MPMMG) INVENTOR. ALBERT mzv WEEL AGEWI Patented Apr. 8, 1952 MIXING CIRCUIT ARRANGEMENT Adelbert van Weel, Eindhoveu, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 20, 1946, Serial No. 685,204 In the Netherlands November 12, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires November 12, 1963 8 Claims.

This invention relates to a mixing circuit ar rangement which is particularly suitable for use on short waves and in which the incoming oscillations are supplied in push-pull and the local oscillations produced by an oscillator are supplied in single phase to the input electrodes of two mixing systems. When transmitting ultrahigh frequencies, this method oifers the advantage that a smaller input damping and a better signalto-noise ratio are obtained.

It has previously been proposed that in such a circuit-arrangement the cathodes of the mixing systems and of one or more discharge systems used in the local oscillator, should be mutually connected. In this case the various discharge systems may be housed in a single discharge tube. It is then sometimes not possible to connect the junction of the cathodes directly to a point of constant potential, such as ground, because the said junction is connected to the corresponding connecting pin of the discharge tube through a comparatively long connecting lead. In the case of short waves, this connecting lead constitutes a considerable inductance which is included in the cathode lead of the'local oscillator causing a considerable negative feed-back, due to which the oscillator circuit can be set into oscillation only with great difficulty, if at all.

In order to avoid this difiiculty, it is necessary to include a definite impedance, generally one having a high value, between the connecting pin and. ground. However, as will appear hereinafter, the employment of such a high impedance entails the drawback that the voltage having the frequency of the local oscillations which is set up between the input electrodes of the mixing systems cannot be raised to a high value without any further expedients. The invention provides a means whereby this difficulty is prevented and whereby the local oscillations produced can be supplied efiicaciously to the mixing systems.

According to the invention, between the junction of the cathodes and a point having a constant potential there is "included a first impedance which forms part of a single-phase circuit constituted by the parallel-connected impedances of the two halves of the push-pull circuit, the parallel-connected input impedances of the mixing systems, and the impedances common to the input circuits of these systems. The single phase circuit is tuned in such a manner that a maximum voltage having the frequency of the local oscillations is set up between the mixer electrodes.

That branch of the single-phase circuit which extends from the said junction via the mixing 2 systems to the point of constant potential pref.- erably includes a second impedance. The values of the first and second impedances are adjusted in such a manner that a maximum voltage having the frequency of the local oscillations is set up between the mixer electrodes. It is also possible to include a network between the junction of the cathodes and/or the point of constant potential on the one hand and the input electrodes not directly connected to each other and/or the points of connection of the aerial on the other hand, and to adjust this network and the said first impedance in such a manner that a maximum voltage having the frequency of the local'oscillations is set up between the mixer electrodes.

As a rule, the push-pull circuit constituted by the impedances included between the input electrodes not directly connected to each other is tuned to the frequency of the incoming oscillations.

The oscillations received by the antenna may be transmitted to the push-pull circuit either directly or via an amplifier; the points of connection of the antenna and of the amplifier are preferably chosen such that a voltage node for the local oscillation frequency occurs at these points. This prevents the antenna from reradiating the local oscillations and the amplifier from acting upon the tuning of the single-phase circuit. a

In order that the invention may be clearly understood and readily carried into effect, it will now be explained more fully with reference to the accompanying drawing.

Figure 1 shows a circuit embodying the invention as applied to a mixing circuit;

Figure 2 shows an arrangement corresponding to the general scheme of Figure 1 and in addition showing the added impedances Z3, Z3", and Z4, by which it is possible to adjust the position of the node of voltage of the intermediate frequency to coincide with the point of connection of the antenna, 13, D", thereby eliminating reradiation;

Figure 3 shows a further embodiment of the invention wherein the impedances Z3, Zs",,and Z4 are replaced by a single impedance Z3;' and Figure 4 shows an embodiment of the invention wherein a resonant circuit is coupled between the antenna connections and ground.

Figure 1 shows a mixing circuit arrangement which forms part of a superheterodyne receiver applied. 7 The oscillations received by' a dipolar antenna D, D are supplied to two conductors L1, L1, which jointly constitute a Lecher system which may be tuned to the frequency of the incoming oscillations by means of a short-circuiting bridge K. The Lecher system L1, L1, is connected to the anodes of two diode mixing tubes T1, T1. The antenna D, D is so connected to the Lecher system L1, L"1, as to obtain the correct matching of the antenna to the mixing tubes T1, T1". The input impedance of the mixing tubes are constituted by the capacities C1, C1.

The local oscillations are produced by a local oscillator O. This oscillator is constituted by a triode T2 and an oscillatory circuit which is constituted by a capacity C2 and an inductance L2 and which is included between the control grid and the anode of the triode T2.

The cathodes of the two mixing diodes T1, T1, and the cathode of the oscillatory triode T2 are connected to one another at point P. The junction P is connected to earth via a variable impedance Z1; the short-circuiting bridge K is connected to earth through a variable impedance Z2.

A resonant circuit tuned to the intermediate frequency and constituted by a coil L4 and a condenser C4 is connected in push-pull to the anodes of the two diodes via two high-frequency chokes L3, L3". The chokes are provided for the purpose of preventing transmission ofthe incoming high-frequency oscillations to the parts of the receiver following the mixing stage. A leakage resistance R1 is included between the middle of the coil L4 and ground. The intermediate-frequency circuit 114-04 is separated from the pushpull circuit by two blocking condensers C3, C3". The coil L4 is in addition coupled inductively to a second intermediate-frequency circuit L5, Cs from which the output voltage of the circuitarrangement is taken. For clearness sake the direct-current sources are omitted in th figures.

In order to set the local oscillator into oscillation a sufficiently high impedance must exist between point P and ground. The value of this impedance is determined both by the value of the variable impedance Z1 and the value of the impedance between point P via the diodes T1, T1", to ground. As the value of this impedance is made higher, the local oscillator oscillates more satisfactorily and a higher voltage of the frequency of the local oscillations is set up across the impedance Z1.

According to the invention, this voltage is supplied to the mixing stage, more particularly to the two diodes T1, T1",'by arranging in parallel with the impedance Z1, the push-pull connected diodes, the Lecher system L1, L1, the short circuiting bridge K, and the variable impedance Z2. If the impedance Z1 could be regarded as a source for the local oscillations whose internal resistance is negligible, the voltage of the local oscillations set up across the diodes T, T would be maximized if the described series-connection arranged in parallel with the impedance Z1 were tuned to the frequency of the local oscillations. This is so because if this series-connection, which is constituted by the parallel-connected impedances of .thetwo halves of the push-pull circuit (L1, L1"; C3103), the parallel-connected input impedances of the two discharge systems '(C1', C1) and the impedance Z2, is in resonance for the frequency of the local oscillations, a maximum voltage of the frequency of the local oscillations is set up across the diodes. In this case,

however, a series-connection is provided between point P and earth, which connection has a very small impedance for this frequency, due to which the local oscillator stops oscillating. To prevent this, and to obtain nevertheless as high a voltage of the frequency of the local oscillations as possible across the diodes, the whole single .phase circuit, in the present case the said series-connection together with the variable impedance Z1, is tuned in such a manner that a maximum voltage of the frequency of the local oscillations is set up between the input electrodes of the diodes.

In the circuit-arrangement shown in Figur 1 this is achieved by including an impedance Z2 in the right branch of the single-phase circuit, i. e. the said series-connection between point P and earth, and by adjusting the impedances Z1 and Z2 in such a manner that a voltage maximum is set up across the diodes.

If the single-phase circuit is adjusted to a voltage maximum by means of the impedances Z1 and Z2, there is in general between point P and earth an impedance which may be constituted by an inductance or a capacity, since the circuit is, as a rule, not tuned to the frequency of the local oscillations. However, in certain cases it may be necessary to tune the singlephase circuit to this frequency in order to obtain a maximum voltage across the diodes. In this case there is a tuned circuit between point P and earth, which behaves like a real resistance for the frequency of the oscillator.

As a rule, it is still desirable to arrange the antenna in a voltage minimum for the frequency of the local oscillations without disturbing the optimum adaptation of the antenna to the mixing tubes. Figure 2 shows a circuit-arrangement by which this can be achieved.

In the circuit shown in Figure 2 the discharge systems T1, T1 and T2 are housed in one discharge tube T3. Furthermore, between the two halves of the push-pull circuit, viz. between the two anodes of the diodes and ground there is included a network constituted by the series-connection of two impedances Z3, Z3, whose junction is grounded through an impedance Z4. In a practical form of construction, the impedances Z3, Z3" may be inductance coils and the impedance Z4 a condenser.

The push-pull circuit is tuned to the frequency of the incoming oscillations by means of the short-circuiting bridge K. The inductance of the coils Z3, Z3" is given so high a value that their presence has little or no influence on the tuning of the push-pull circuit. The antenna D, D" is connected to the Lecher system L1, L1 so as to obtain the optimum adaptation, i. e. maximum signal-to-noise ratio or maximum amplification, of the antenna to the mixing systems. Now the impedance Z2 is adjusted in such a manner that the points of connection of the antenna exhibit a voltage minimum for the frequency of the local oscillations, i. e. that the parallel-connected right halves of the Lecher leads L1, L1, taken from the points of connection of the antenna, jointly with theimpedance Z2 are tuned to the frequency of the local oscillations. Finally, the condenser Z4 is adjusted in such a manner that the maximum voltageof the frequency of the local oscillations is set up across the diodes.

Instead of providing the described network, it

frequently sufiices to include a variable impedance between the anodes of the diodes. In this case the maximum voltage across the diodes is Z1 and Z2.

sents the variable impedance included between the mixer anodes.

For connecting the antenna in a voltage minimum for the frequency of the local oscillations it is alternatively possible to include a resonant circuit tuned to this frequency between the points 'of connection of the antenna and earth. Such a circuit may be constituted, for example, by

two series-connected coils or condensers which are-included between the said points of connec tion and whose junction is earthed through a condenser or a coil. Such a circuit is illustrated in Fig. 4, where coils Lo and Le" are connected in series between the junction points of antenna D, D" and Lecher-line L1, L1 and a condenser 06 is connected between the junction of coils Ls and L6" and ground.

What I claim is:

1. A circuit arrangement for mixing a first wave and a second wave to produce anlintermediate frequency wave, comprising a pair of said first wave, a network tuned to the frequency 'of said intermediate frequency wave and having j,an electrical center and coupled between the anode electrodes of said mixing elements, andan impedance element connected between said electrical center and ground.

,3. A circuit arrangement for mixing a first ,wave and a second wave to produce an intert-mediate frequency wave, comprising a air of mixing elements each having anode and cathode electrodes, a Lecher-system having an open end thereof coupled to the anode electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first ing a cathode, means to couple together the cathwave including an electron discharge system havodes of said mixing elements and the-cathode of said discharge system to define a junction, means t apply said second wave to said Lecher-system mixing elements each having input and cathode electrodes, a, Lecher-system having an open end thereof coupled to the input electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first 'wave including an electron discharge system having a cathode, means to couple together the cathodes of said mixing elements and the cathode of said discharge system to define a junction,

lmeans to apply said second wave to said Lechersystem, a first impedance network coupled between said junction and a point of constant potential, a second impedance network coupled between the closed end of said Lecher-system and said point of constant potential, the relative impedance values of said first and second impedance "networks being adjustable to maximize the voltage produced across said mixing elements by said first wave, a network having an electrical center and coupled between the input electrodes of said mixing elements, and an impedance element connected between said electrical center and said point of constant potential.

2. A circuit arrangement for mixing a first wave and a second Wave to produce an intermediate frequency wave, comprising a pair of mixing elements each having anode and cathode at a point of voltage node of said" first wave, a first impedance network coupled between said junction and a point of constant potential, -a

second impedance network coupled between the closed end of said Lecher-system and said point .of constant potential, the relative impedance nected between said electrical center and said point of constant potential.

4. A circuit arrangement for" mixinga first wave and a second wave to produce an intermediate frequency wave, comprising a'pair' of mixing elements each having input and cathode electrodes, a Lecher-system having an open end thereof coupled to the input electrodes of said mixing elements in push-pull relationship and having aclosed end, means to generate said first wave including an electron discharge system having a cathode, said mixing elementsfand said discharge system being included in an electron discharge tube, means to couple together the cathodes of said mixing elements and the cathode of said discharge system to define a junction, means to apply said second wave to said Lechersystem, a first impedance network coupled between said junction and a point of constant potential, a second impedance network coupled be,- tween the closed end of said Lecher-system and said point of constant potential, the relativeimpedance values of said first and second impedance networks being adjustable to maximize the voltage produced across said mixing elements by said firstwave, a network having an electrical center and coupled between the input electrodes oflsaid mixing elements, and an impedance element, connected between said electrical center and said point of constant potential,

, mediate frequency wave, comprising a pairs-of of said discharge system to define a junction,,.

means to apply said second wave to said Lechersystem, a first impedance network coupled between said junction and ground, a second impedance network coupled between the closed end N of said Lecher-system and ground, the relative impedance values of said first and second impedance networks being adjustable to maximize the voltage produced across said mixing elements by mixing elements each having anode and cathode electrodes, a Lecher-system having an open end thereof coupled to the anode electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first wave including an electron discharge system having cathode, control grid and anode electrodes and an oscillatory circuit tuned to the frequency of said first wave coupled between the control grid and anode electrodes of said discharge system, means to couple together the cathodes of said. mixingelements and'the cathode of said discharge system to define a junction, means to apply said second wave to said Lecher-system, azfirst impedance network coupled between said junction and a point of constant potential, a second impedance network. coupled between the closed end of said Lecher-system and said point of constant potential, the relative impedance values of said first and second impedance networks being adjustable to maximize the voltage produced'across said mixing elements by said first wave, a network having an electrical center and'coupled between the anode electrodes of said mixing elements, and an impedance element connected between said electrical center and said point of constant potential.

6. A circuit arrangement for mixing a'first wave and a second wave to produce an intermediate frequency wave, comprising a pair of mixing elements each having anode and cathode electrodes, a Lecher-system having an open end thereof coupled to the anode electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first wave including an electron discharge system having a cathode, means to couple together the cathodes of said'mixing elements and the cathode of'said discharge system to define a junction, means to apply said second wave to said Lechersystem, a first impedance network coupled between said junction and a point of constant potential, a second impedance network coupled between the closed end of said Lecher-system and said \point of constant potential, the relative impedancevalues of said first and second impedance networks beingadjustable to maximize the voltage produced across said mixing elements by'said firstwave, a network having an electrical center and coupledbetween the anode electrodes of'said mixing elements, a first impedance element, connected between the electrical center and said point of constant potential, and a third impedance, network including second and third impedance elements coupled in series between the anodesof said mixing elements and a, fourth impedance element coupled between the junction of said second and third impedance elements and said. point ofv constant potential.

7. A circuit arrangement for mixing a first wavejand a second wave to produce anintermediate, frequency wave, comprising a pair of mixing elements each having anode and cathode electrodes, a Lecher-system having an open end thereof coupledto the anode electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first wave including an electron discharge system having a cathode, means to couple together the cathodes of said mixing elements and the cathode of said discharge system to, define a junction, means to apply said second wave to said Lechersystem, a first impedancenetwork coupled between said junction and a point of constant potential, a second impedance network coupled between the closed end of said Lecher-system and said point of constant potential, the relative impedance values of said firstv and second impedance networks being adjustable to maximize the voltage produced across said mixing elements by said first wave, a network having an electrical center and coupled between the anode electrodes of said mixing elements, an impedance element connected between said electrical center and said point of constant potential, and an adjustable impedance element coupled between the anodes of said mixing elements.

8. A circuit arrangement for mixing a first wave and a second Wave to produce an intermediate frequency wave, comprising a pair of mixing elements each having anode and cathode electrodes, a Lecher-system having an open end thereof coupled to the anode electrodes of said mixing elements in push-pull relationship and having a closed end, means to generate said first wave including an electron discharge system having a cathode, means to couple together the cathodes of said mixing elements and the cathode of said discharge system to define a junction, means to apply said second wave to said Lechersystem at points of voltage node of said first wave, a first impedance network coupled between said junction and a point of constant potential, a second impedance network coupled between the closed end of said Lecher-system and said point of constant potential, the relative impedance values of said first and second impedance networks being adjustable to maximize the voltage produced across said mixing elements by said first wave, a network having an electrical center and coupled between the anode electrodes of said mixing elements, a first impedance element connected between said electrical center and said point of constant potential, second and third impedance elements coupled in series between said points of voltage node on said Lecher-system, and a fourth impedance element coupled between the junction of said second and third impedance elements and said point of constant potential.

ADELBERT VAN WEEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,968,610 Mathieu July 31, 1934 2,285,372 Strutt June 2, 1942 2,307,074 Pray et al Jan. 5, 1943 2,382,693 Dallenbach Aug. 14, 1945 2,410,387 Mueller Oct. 29, 1946 2,434,474 Strutt Jan. 13, 1948 2,441,452 Strutt et al May 11, 1948 2,453,078 Posthumus Nov. 2, 1948 2,479,537 Fyler Aug. 16, 1949 FOREIGN PATENTS Number Country Date 554,675 Great Britain July 14, 1943 

